Solar radiant energy absorption from the exterior surfaces of buildings is often undesirable, especially in residential and commercial buildings in warmer climates, as it decreases comfort and increases cooling costs. Instead, high solar reflectivity exterior surfaces (those with high TSR values, as measured on a 0-100% scale) are desirable in order to keep buildings cooler in the sun, and so reduce cooling and energy costs. Some areas of the country now have voluntary or involuntary standards for minimum TSR levels for new roofing materials. In some cases, these minimum TSR levels are as high as 70%, meaning that in practice it has only been possible to meet the standards by using white, or very pale colored, roofing materials. For aesthetic reasons, it would be desirable to use a variety of colors, including darker and brighter colors, in roofing materials.
Many publications about “cool roof coatings” describe the conventional wisdom that TSR properties are primarily determined by the reflective properties of the pigment(s) used in the topcoat (cf. a recent paper by M. Zheng and K. Wood, appearing in Finishing Today magazine). This paper claims that small improvements (2-3% absolute) in TSR can be obtained by using KYNAR PVDF based coatings instead of conventional resins.
Surprisingly, it has now been found that a colored topcoat, over a high TSR underlayer can be formulated to produce a high TSR, colored composition. This multi-layered composition can be used to coat roofs and walls of buildings, thus providing a variety of useful colors, while maintaining a high TSR.